This invention relates to additive compositions, lubricating oil compositions containing said additive compositions, and a process for manufacturing said additive compositions. More specifically, it relates to metal diaryl dithiophosphates and their manufacture and use.
It is well known that various additives can be added to lubricating oils in order to improve various oil properties and to make a more satisfactory lubricant. Antiwear agents are intended to decrease wear of machine parts. Wear inhibitors for incorporation in motor oils and industrial oils are finding greater use as a result of greater stress placed on moving parts in high performance engines. Numerous additives have been developed for use in such oil compositions to improve the lubricating characteristics thereof and thereby to lessen the wear of the moving parts.
Metal diaryl dithiophosphates, especially zinc diaryl dithiophosphates, have long been used as antiwear additives and antioxidants in hydraulic oils, motor oils and automatic transmission fluids. In the manufacture of such metal diaryl dithiophosphates, an aryl dithiophosphoric acid is commonly neutralized with a base, such as zinc oxide or hydroxide. This neutralization step does not take place readily and commonly a large excess of the base is used in conjunction with a neutralization promoter and high neutralization temperatures. Sometimes the use of promoters such as nitric acid can lead to undesirable side effects. In many cases the neutralized product is difficult to filter and has a dark color. The effectiveness of a compound as a neutralization promoter is difficult to predict and therefore such promoters are generally determined on an empirical basis.
It is an object of this invention to provide an improved process for the manufacture of metal diaryl dithiophosphates.
It is an object of this invention to provide a process for the manufacture of metal diaryl dithiophosphates wherein less excess metal base is required for the neutralization of dithiophosphoric acids.
It is an object of this invention to provide a process for the manufacture of metal diaryl dithiophosphates using lower neutralization temperature or shorter neutralization time.
It is an object of this invention to provide a process for the manufacture of metal diaryl dithiophosphates wherein the neutralized product has a light color and high filtration rates.
It is further an object of this invention to provide a highly effective antiwear and antioxidant additive for use in lubricating oils.